Patent GB-428622-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/42
Filed: 1933-11-18
Abstract: 428,622. Automatic and semi-automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, London, and LONG, D. P., 11, Marlings Park Avenue, Chislehurst, Kent. Nov. 18, 1933, No. 32198. Addition to 382,964. [Class 40 (iv)] In a system incorporating a normally metallically byepassed feed bridge circuit which precedes the final selector and which is adapted to be inserted due to the connection of battery to the test wire when the final selector switches through, as described in the parent Specification, the insertion of the feed bridge is prevented when the call is set up by a toll operator at the same or at a distant exchange by grounding of the test wire at a circuit which precedes the first selector and which supplies feed current in this case. The second and final selectors carry both local and toll traffic, and it is arranged that busy flash battery flashes the toll operator's supervisory lamp when applied at the final selector, but not when applied at a group selector, the operator merely hearing busy tone in the latter case. In response to a signal from the operator, the final selector re-operates to establish a speaking connection to a busy line and waits thereon until it becomes free, whereupon the line is seized without further action on the part of the operator. First selector, Figs. 3, 4. This is capable of use as a local first selector or as a toll first selector. It may receive one or two digits before hunting. Relay WS(i) energizes upon seizure and grounds the start wire to operate ST in the common control circuit. Relay GP is operated as long as the control circuit is free, and when it falls back extends the start wire over chain contacts gp1 to another free control circuit. The switch CS rotates to associate the control circuit with the seized selector, when relay TB energizes in series with K and connects up TC. The line wires are transferred to line relay A, which connects up B, SD and dialling tone is sent back. The digit switch DS is set by the first digit, dialling relay C pulling up at the first impulse and disconnecting SD. The relevant terminals of bank DS1 are cross-connected to terminals TE1-8, and when C falls back one or more relays are selectively operated to determine the subsequent operation. If one of terminals TE1-4 is marked, R rotates and initiates immediate hunting of the selector, while if one of terminals TE5-7 is marked, SD operates and advances the switch DS to a sub-normal position in readiness for the reception of a second digit. In the former case, relay 7 controls wiperswitching relay WS in the selector, while S controls the sending forward of a discriminating signal. In the latter case, relay Y determines whether the switch DS shall stop in position 11 or 12, while PP, PA if operated control the advance of the selector through 180‹ to a sub-normal position, connect up wipers DS2, 6, 8 in place of DS1, 5, 7 and cause the switch DS to take two steps per impulse instead of one in response to the second digit by means of circuits over wiper DS4. The terminals of banks DS1, DS2 which are effective after the second digit are cross-connected to terminals TE1-4, so that relay R initiates hunting of the selector, while Y, S may operate as before. If an idle line is found in the group marked over wiper DS5 or 6, test relay T energizes followed by G, TA and switching relay H operates, ground being applied to the positive wire if S is up pending release of the control circuit. If no idle line is found, T energizes in the last position in series with LC which connects up busy tone, TA being inoperative in this case. Upon release, an overflow meter is actuated over wiper DS7 or 8. If an unallotted digit is received, TE8 is marked and R energizes in series with Z. The selector rotates to its last position and LC now connects up NU tone. If no impulses are received, relays S, Z operate after an interval and connect up R. The selector rotates and stops in its penultimate position since the switch DS is at normal, and the line is switched through to relay PG, which closes an alarm circuit. Second selector, Figs. 5, 6. Line relay A energizes followed by release relay B, guard relay JB and coupling relay K, while P energizes over the loop provided signal ground is not connected to the positive wire and connects up PP which advances the selector through 180‹ to a sub-normal position and steps the digit switch DS to its first position. In response to the received digit, the switch DS takes two steps per impulse starting from normal if PP is back or from the first position if PP is up. Dialling relay C connects up SG, and at the end of the train C, PP relapse and disconnect SG(i). The terminals of bank DS1 are cross-connected to terminals TE1-6 or are left disconnected. Wiper-switching relay WS operates if TE2 or 4 is marked, while relay D which controls the sending forward of a discriminating signal operates if TE4, 5 or 6 is marked. If TE3 or 5 is marked, WS operates and falls back after the sluggish relapse of SG, thus enabling a split group to be searched. In all cases relay R energizes and starts the selector which searches over the group marked by wiper DS3, and relays T, G, TA energize when an idle line is found and connect up switching relay H. If no idle line is found, the selector stops in its last position and LC sends back busy tone and flash and actuates an overflow meter over wiper DS7. If a spare digit is received, SG(ii) holds over TE1 in series with WS, and the selector rotates to its last position (no marking being applied) and in this case NU tone is connected up. The control circuit serves two groups of selectors, wipers and banks DS1, 3, 7 being appropriate to one group and DS2, 4, 8 to the other. Feed bridge, Fig. 7, and final selector, Figs. 8, 9 (not shown). Through metallic circuits normally exist over the speaking and test wires to the final selector. The latter, which is adapted for hunting over P.B.X. lines and is provided with breaking-in facilities, is identical with the final selector described in Specifications 412,722 (Figs. 2, 3) and 417,461. When the switching relay operates in the final selector, battery is returned over test wire P and ground over wire BS, and relay H responds provided the call is a local one. In the case of a toll call, however, H is short-circuited by ground connected to wire P through RC, Fig. 2, as described later, and the bridge circuit remains in its present condition. Release relay B energizes and connects up metering relay J and line relay A which applies ringing current. Ring- trip relay F operates on reply, followed by back-bridge relay D, and H, J fall back. Relay F separates the incoming and outgoing wires P and grounds the latter. If the calling party clears first, a circuit is made for thermal relay TH, which upon operation disconnects F and brings about release of the final selector should the called party fail to hang up. If the called party clears first, D falls back and lights lamp CSH in series with a delayed alarm relay. Toll call set up by distant operator, Figs. 1, 2. The junction from the toll exchange, Fig. 1, terminates in the repeater, Fig. 2, which precedes the first selector, Fig. 3. When the operator plugs into jack OJ, sleeve relay S energizes, followed by SS, which loops the junction. Relay IL, DA respond in series with line relay A, Fig. 2, differential relay DR being inoperative. Release relay B energizes and connects battery and ground through PS NS to the outgoing line wires to seize the first selector, the former relay responding at once in series with WS, Fig. 3, and the latter as soon as the line wires are transferred to A, Fig. 4. Relay G energizes and reverses the current over the junction to release polarized relay DA, Fig. 1, and flash the supervisory lamp in the sleeve circuit. Speaking and dialling keys are actuated, connecting battery to the tip and ring of the plug and a high resistance to the sleeve, whereupon relays DT, DU operate through the medium of RR and complete the impulse repeating circuit. Resistance YB is short-circuited over strapped terminals SA, SB except in the case of low resistance junctions. Dialled impulses are repeated forward by A, Fig. 2, and upon restoration of the dialling key LR energizes in the sleeve circuit and disconnects DT, DU. The supervisory lamp remains alight over S(i) as long as IL is operated. If an idle line is seized, PS, NS, Fig. 2, fall back while the switching relays of the selectors hold to ground connected to test wire P through RC, which operates and connects up DF. Operation of the ringing key connects up RR, Fig. 1, which grounds the negative wire to energize DR, Fig. 2, and R applies ringing current until cut off by F when the called party replies. Toll busy tone is connected to test wire P. Back bridge relay D operates and disconnects G to reoperate supervisory relay DA, Fig. 1. Busy flash from the final selector releases PS intermittently and LF responds in synchronism and repeats the condition over the junction to IL which flashes the supervisory lamp. Busy flash from a group selector, however, is not repeated since it is out of phase with the interrupter controlling LF, and the operator merely hears busy tone. Operation of the ringing key causes DR to pull up as before, but in this case TO energizes, since NS is still up. Test wire P is connected to the junction so that toll busy tone may be heard if the line is engaged in a toll call. Different tones may be used to denote calls of varying importance. Reversed battery is applied to the positive wire during the operating period of DF to enable the operator to break in, causing release of an operated relay in the final selector, as described in Specification 412,722, the talking circuit being completed when TO falls back upon restoration of the ringing key. When the call is accepted, PS, NS fall back as in a call to an idle line. Toll call set up by local op